This invention relates to a process for recovering symmetrical diglycerides of fatty acids from glyceride mixtures. More particularly, it relates to a process for recovering symmetrical diglycerides of high purity from glyceride mixtures by a simple crystallization method.
The preparation of symmetrical diglycerides of fatty acids has been described in the prior art. These diglycerides are of particular value in the preparation of cocoa butter substitutes which can be employed to advantage in the manufacture of confections and cosmetic materials. Symmetrical diglycerides of fatty acids can be formed by several techniques which, in general, include the partial esterification of free fatty acids with glycerol, the partial hydrolysis of fatty triglycerides, and the glycerolysis of fatty triglycerides. These methods, while effective to provide symmetrical diglycerides, result in the production of a mixture containing mono-, di-, and triglycerides and the relative proportions of these glycerides will depend upon relative proportions of reactants and the particular reaction conditions employed. The desirable separation of symmetrical diglycerides from such mixtures, as has been pointed out in Great Britain Pat. No. 1,325,924, is only achieved with some difficulty.
One approach to the provision of pure symmetrical diglycerides of fatty acids has involved the employment of a separation technique based upon the use of two liquid solvent phases. Thus, the U.S. patent of E.R. Lowrey (U.S. Pat. No. 3,826,720, issued July 30, 1974) describes a process whereby a glycerolysis mixture of mono-, di-, and triglycerides is subjected to a liquid-liquid extraction process to provide an aqueous-methanol phase rich in monoglyceride and a hexane phase rich in diglycerides and triglycerides. Liquid-liquid extraction methods are, however, relatively complex in operation, require considerable capital expenditure, and require high ratios of solvent to glyceride mixture. Moreover, the liquid/liquid separation process still necessitates recovery of the desired symmetrical diglyceride from the triglyceride also present in the hexane phase.
Another approach to the provision of symmetrical digylcerides has involved the recovery of the diglyceride from equilibrium mixtures having the desired diglyceride in high concentrations, e.g., in amounts to 90% or higher by weight of the glyceride mixture. In general, the higher the concentration of a given glyceride compound in a mixture of glycerides, the higher its saturation temperature. Consequently, a glyceride mixture having a high concentration of symmetrical diglyceride and only low concentrations of other glycerides, e.g., 1-monoglyceride, will permit crystallization of the desired symmetrical diglyceride from the glyceride mixture, e.g., by cooling, with recovery of product relatively free of other glycerides present in the mixture.
The provision of glyceride mixtures having a high concentration of symmetrical diglyceride and only low concentrations of other glycerides, while more readily adapted to efficient recovery of diglyceride, are not readily prepared without recourse to time-consuming procedures or methods requiring careful control of reaction conditions or parameters. The patents to Lange et al. (U.S. Pat. No. 2,626,952, issued Jan. 27, 1953) and Dutton et al. (U.S. Pat. No. 3,012,890, issued Dec. 12, 1961), for example, describe methods for recovering symmetrical diglyerides from glyceride equilibrium mixtures based upon multiple crystallizations at different temperatures. Pure diglyceride is obtained in high yield and purity by subsequent recrystallizations from solvents including mixtures of polar and non-polar solvents.
Similarly, the U.S. Pat. Nos. of Harwood (3,312,724, issued Apr. 4, 1967, and 3,634,473, issued Jan. 11, 1972) describe methods for the preparation of symmetrical fatty diglycerides. These methods involve careful control of reactant concentrations and equilibrium conditions to prepare glyceride mixtures having diglyceride in a high concentration. The separation of the diglyceride component is then accomplished by crystallization from a solvent such as a mixture of isopropyl alcohol and petroleum ether. The processes of the Harwood patents require the employment of controlled reaction and equilibrium conditions to produce diglyceride in the high concentrations permitting ready separation. Frequently, however, it will be desired to provide glyceride mixtures by glycerolysis reaction routes which permit considerable latitude in the control of reaction parameters. The recovery of symmetrical diglycerides from such mixtures which may contain the desired diglycerides in amounts only up to about 50% by weight of the mixture and may have an appreciable 1-monoglyceride content, e.g. from 8% or more, are especially difficult to separate by crystallization. Typical of such mixtures are the relatively crude products obtained by conventional glycerolysis of triglycerides, i.e., by the reaction of glycerol with fatty triglyceride. Such mixtures are described, for example, in the patent of Lowrey (U.S. Pat. No. 3,826,720, issued July 30, 1974).
It is an object of the present invention to provide a method for the recovery of symmetrical diglycerides of free fatty acids from mixtures of fatty glycerides.
Another object of the invention is the provision of a process for recovering symmetrical diglycerides of fatty acids from relatively crude glyceride mixtures.
Still another object of the present invention is the provision of a process for recovering symmetrical diglycerides of high purity from glyceride mixtures in a single crystallization step and from glyceride mixtures which can be prepared without the need for particular or carefully controlled reaction conditions.
These and other objects of the invention and the method by which they are accomplished will become apparent from consideration of the more detailed description hereinafter.